Section 1 Characteristics of the Atmosphere s1

Chapter 22 Notes Section 1 Characteristics of the Atmosphere- Composition of the Atmosphere  atmosphere a mixture of gases that surrounds a planet, such as Earth • The most abundant elements in air are the gases nitrogen, oxygen, and argon. • The two most abundant compounds in air are the gases carbon dioxide, CO2, and water vapor, H2O. • In addition to containing gaseous elements and compounds, the atmosphere commonly carries various kinds of tiny solid particles, such as dust and pollen. Nitrogen in the Atmosphere • Nitrogen makes up about 78% of Earth’s atmosphere and is maintained through the nitrogen cycle. • Nitrogen is removed from the air mainly by the action of nitrogen-fixing bacteria. • Decay releases nitrogen back into the atmosphere. Oxygen in the Atmosphere • Oxygen makes up about 21% of Earth’s atmosphere. • Land and ocean plants produce large quantities of oxygen in a process called photosynthesis. • Animals, bacteria, and plants remove oxygen from the air as part of their life processes. Water Vapor in the Atmosphere • As water evaporates from oceans, lakes, streams, and soil, it enters air as the invisible gas water vapor. • Plants and animals give off water vapor during transpiration, one of their processes. But as water vapor enters the atmosphere, it is removed by the processes of condensation and precipitation. • The percentage of water vapor in the atmosphere varies depending on factors such as time of day, location, and season. Ozone in the Atmosphere  ozone a gas molecule that is made up of three oxygen atoms • Ozone in the upper atmosphere forms the ozone layer, which absorbs harmful ultraviolet radiation from the sun. • Without the ozone layer, living organisms would be severely damaged by the sun’s ultraviolet rays. • Unfortunately, a number of human activities damage the ozone layer. Particulates in the Atmosphere • Particulates can be volcanic dust, ash from fires, microscopic organisms, or mineral particles lifted from soil by winds. • Pollen from plants and particles from meteors that have vaporized are also particulates. • Large, heavy particles remain in the atmosphere only briefly, but tiny particles can remain suspended in the atmosphere for months or years.

Atmospheric Pressure atmospheric pressure the force per unit area that is exerted on a surface by the weight of the atmosphere • Atmospheric pressure is exerted equally in all directions—up, down, and sideways. • Because the pull of gravity is not as strong at higher altitudes, the air molecules are farther apart and exert less pressure on each other at higher altitudes. • Thus, atmospheric pressure decreases as altitude increases. • Atmospheric pressure also changes as a result of differences in temperature and in the amount of water vapor in the air. • In general, as temperature increase, atmospheric pressure at sea level decreases.  Similarly, air that contains a lot of water vapor is less dense than drier air because water vapor molecules have less mass than nitrogen or oxygen molecules do. Layers of the Atmosphere 1. troposphere the lowest layer of the atmosphere, in which temperature drops at a constant rate as altitude increases; the part of the atmosphere where weather conditions exist 2. stratosphere the layer of the atmosphere that lies between the troposphere and the mesosphere and in which temperature increases as altitude increases; contains the ozone layer  In the upper stratosphere, the temperature increases as altitude increases because air in the stratosphere is heated from above by absorption of solar radiation by ozone. 3. mesosphere the coldest layer of the atmosphere, between the stratosphere and the thermosphere, in which the temperature decreases as altitude increases 4. thermosphere the uppermost layer of the atmosphere, in which temperature increase as altitude increases; includes the ionosphere  Interactions between solar radiation and the ionosphere cause the phenomena known as auroras.  However, above the ionosphere is the region where Earth’s atmosphere blends into the almost complete vacuum of space.

Temperature Inversions • Any substance in the atmosphere and that is harmful to people, animals, plants, or property is called an air pollutant. • Today, the main source of air pollution is the burning of fossil fuels, such as coal and petroleum. • Certain weather conditions can make air pollution worse. • One such condition is a temperature inversion, the layer of warm air on top of cool air.

Section 2 Solar Energy and the Atmosphere The Atmosphere and Solar Radiation • As solar radiation passes through Earth’s atmosphere, the atmosphere affects the radiation in several ways. • Most of the solar rays that reach the lower atmosphere, such as visible and infrared waves, have longer wavelengths. • Clouds, dust, water droplets, and as molecules in the atmosphere disrupt the paths of radiation from the sun and cause scattering • As solar radiation passes through Earth’s atmosphere, the atmosphere affects the radiation in several ways. • Most of the solar rays that reach the lower atmosphere, such as visible and infrared waves, have longer wavelengths. • Clouds, dust, water droplets, and as molecules in the atmosphere disrupt the paths of radiation from the sun and cause scattering.

Absorption and Infrared Energy • Solar radiation that is not reflected is absorbed by rocks, soil, water, and other surface materials. • Gas molecules, such as water vapor and carbon dioxide, in the atmosphere absorb these infrared rays. • The absorption of thermal energy from the ground heats the lower atmosphere and keeps Earth’s surface much warmer than it would be if there were no atmosphere. greenhouse effect • the warming of the surface and lower atmosphere of Earth that occurs when carbon dioxide, water vapor, and other gases in the air absorb and reradiate radiation • Earth’s atmosphere slows the escape of energy that radiates from Earth’s surface. Human Impact on the Greenhouse Effect • Generally, the amount of solar energy that enters Earth’s atmosphere is about equal to the amount that escapes into space. • However, human activities may change this balance and may cause the average temperature of the atmosphere to increase. • Increases in the amount of carbon dioxide may intensify the greenhouse effect and may cause Earth to become warmer in some areas and cooler in others. Variations in Temperature • Radiation from the sun does not heat Earth equally at all places at all times. • Earth’s surface must absorb energy for a time before enough heat has been absorbed and reradiated from the ground to change the temperature of the atmosphere. • The temperature of the atmosphere in any region on Earth’s surface depends on several factors, including latitude, surface features, and the time of year (how direct the light is) and length of day.

Latitude and Season • Latitude is the primary factor that affects the amount of solar energy that reaches any point on Earth’s surface. • Because Earth is a sphere, the sun’s rays do not strike all areas at the same angle. • Thus, the energy that reaches the equator is more intense than the energy that strikes the poles, so average temperatures are higher near the equator than near the poles.

Water in the Air and on the Surface • Because water vapor stores heat, the amount of water in the air affects the temperature of a region. • Land areas close to large bodies of water generally have more moderate temperatures • The wind patterns in an area also affect temperature. conduction the transfer of energy as heat through a material • The molecules in a substance move faster as they become heated. • Collisions between the particles result in the transfer of energy, which warms the substance. • Thus, conduction heats only the lowest few centimeters of the atmosphere, where air comes into direct contact with the warmed surface of Earth. convection the movement of matter due to differences in density that are caused by temperature variations; can result in the transfer of energy as heat • Convection occurs when gases or liquids are heated unevenly. • The continuous cycle in which cold air sinks and warm air rises warms Earth’s atmosphere evenly.

Section 3 Atmospheric Circulation Global Winds • Each hemisphere contains three looping patterns of flow called convection cells. • Each convection cell correlates to an area of Earth’s surface, called a wind belt, that is characterized by winds that flow in one direction. • These winds are called prevailing winds. trade wind prevailing winds that blow from east to west from 30º latitude to the equator in both hemispheres • Like all winds, trade winds are named according to the direction from which they flow. • In the Northern Hemisphere, the trade winds flow the northeast and are called the northeast trade winds. • In the Southern Hemisphere, they are the southeast trade winds. westerlies prevailing winds that blow from west to east between 30º and 60º latitude in both hemispheres • Between 30º and 60º latitude, some of the descending air moving toward the poles is deflected by the Coriolis effect. • In the Northern Hemisphere, the westerlies are the southwest winds. In the Southern Hemisphere, they are the northwest winds. polar easterlies prevailing winds that blow from east to west between 60 and 90 latitude in both hemispheres • Surface winds created by the polar high pressure are deflected by the Coriolis effect and become the polar easterlies. • Where the polar easterlies meet warm air from the westerlies, a stormy region known as a front forms.

The Doldrums and Horse Latitudes • The trade wind systems of the Northern Hemisphere and Southern Hemisphere meet at the equator in a narrow zone called the doldrums. • As the air approaches 30º latitude, it descends and a high-pressure zone forms. These subtropical high- pressure zones are called horse latitudes. • Since the air is moving vertically at both of these locations there is very little wind.

Wind and Pressure Shifts • As the sun’s rays shift northward and southward during the changing seasons of the year, the positions of the pressure belts and wind belts shift. • Although the area that receives direct sunlight can shift by up to 46 º north and south of the equator, the average shift for the pressure belts and wind belts is only about 10º of latitude. • However, even this small change causes some areas of Earth’s surface to be in different wind belts during different times of the year.

Land and Sea Breezes • Equal areas of land and water may receive the same amount of energy from the sun. However, land surfaces heat up faster than water surfaces do. • The cool wind moving from water to land is called a sea breeze. • Overnight, the land cools more rapidly than water does, and the sea breeze is replaced by a land breeze.

Mountain and Valley Breezes • A valley breeze forms when warm air from the valleys moves upslope. • At night, the mountains cool more quickly than the valleys do. At that time, cool air descends from the mountain peaks to create a mountain breeze. • Areas near mountains may experience a warm afternoon that turns to a cold evening soon after sunset.